I own a cheap Chinese android phone which I use for my everyday tasks and I am having issues with what I understand is malware.

Frequently, Google Play informs me to

Disable harmful app "com.android.service" can damage your device

which I proceed to do but to no avail; this happens around 5 to 10 times in a single day and I suspect it has to do with how often I enable my Wi-Fi and/or restart the device but I could be wrong.

I have installed Malwarebytes, AVGAntivirus and CCleaner. Occasionally, Malwarebytes and AVGAntivirus will identify some malware which will then go on to remove successfully.

I have had these applications occasionally flag something (app?) on my phone entitled launcher3 and Medias which I have unsuccessfully tried uninstalling.

Recently I found out I could restrict "launcher3"'s permissions which I went on and did.

I'm not sure if this is the case but since then, I have been experiencing pop-ups from something (app?) entitled "Shell" with ads and usually when firing Firefox (I don't use Chrome) and/or when I enable my Wi-Fi and/or when I restart my device, Firefox opens a some random add-like tab.

I don't know if it's for the better or for the worse but in the majority of cases whatever ad content I'm being served doesn't display correctly, only partially.

My question is pretty straightforward:

What do I have to do to get rid of all these nuisances and be able to use my phone as intended?